The Bug in the Machine
September 5, 2026 · by White Nights
On September 9, 1947, the Harvard Mark II computer stopped working. This was not unusual — the machine, which filled an entire room and was made of thousands of electromechanical relays, stopped working fairly often. What was unusual was the cause. Engineers tracing the fault to Relay #70 found a moth, its wings caught in the contacts, preventing them from closing.
They extracted it with tweezers and taped it into the operations logbook with a note: "First actual case of bug being found." The log entry is still in the Smithsonian. The handwriting is Grace Hopper's.
Hopper was a mathematician, a naval officer, and one of the most consequential figures in the history of computing. She was among the first programmers of the Mark I, Harvard's earlier machine. She later developed the first compiler — a program that translates human-readable code into machine language — which made it possible for ordinary people to write software without understanding the binary operations underneath. She championed COBOL, the language that ran banking systems for decades.
The word "bug" for a technical fault predates the moth by decades — Edison used it. But Hopper's logbook entry gave the metaphor its most famous moment, and it's the one that stuck.
She retired from the Navy as a Rear Admiral at 79. She said her greatest accomplishment was all the young people she had trained. The moth is still taped to the page.